1. Field of the Invention
The present invention relates to a nonlinear all-optical time division multiplexer and demultiplexer and, more particularly, to an optical multiplexer and demultiplexer formed from a plurality of triggerable switching elements, each switching element comprising a nonlinear optical material disposed in, for example, a ring resonator structure.
2. Description of the Prior Art
A number of recent developments have increased the interest in digital optical signal processing devices and techniques. Laser technology has now advanced to the point that lasers are being used in consumer electronics. Optical fiber communication systems are being widely installed. In the research stage, it has been shown that optical fibers can be used to transmit information at rates approaching 1 THz, as described in the article "Experimental Observations of Picosecond Pulse Narrowing and Solitons in Optical Fibers" by L. F. Mollenauer et al appearing in Physical Review Letters, Vol. 45, No. 1, 1980, at pp. 1095-1097. This rate is much beyond the capabilities of any presently-known electronic light detector. Thus, to utilize this information-handling capacity, some form of optical signal processing will have to be performed before the light signals are converted to electronic ones.
Multiplexing of optical signals onto a single optical fiber has been investigated for over a decade. One exemplary multiplexing arrangement is disclosed in U.S. Pat. No. 3,633,034 issued to T. Uchida et al on Jan. 4, 1969. Here, beams of coherent modulated light which are spatially multiplexed are impinged upon one end of a fibrous converging light guide, each beam having a specific incident angle and position from the axis. This arrangement, therefore, is necessarily limited by the spatial resolution which may be obtained at the entrance to the fiber. The modulated beams are emitted in a spatially multiplexed fashion from the other end of the guide where they are detected.
A scheme which employs time division multiplexing in place of the above-described space-division multiplexing scheme is disclosed in U.S. Pat. No. 3,670,166 issued to I. P. Kaminow on June 13, 1972. In the Kaminow arrangement, time-division multiplexing is achieved by means of a cascaded array of N polarization rotators and associated polarization selective prisms. The N pulse-encoded signals, polarized along a first direction, are coupled bit-by-bit into the respective rotators by means of their associated prisms. The Kaminow arrangement, therefore, requires a large number of dedicated rotators and prisms to achieve a high-capacity system.
Wavelength division multiplexing of optical signals is discussed in the article "Optical Devices for Wavelength Division Multiplexing Systems" by A. M. J. Koonen et al appearing in Philips Telecommunication Review, Vol. 40, No. 2, July 1982, at pp. 102-110. As discussed in the article, signals from several optical transmitters, each emitting at a different wavelength, are combined by a device called a wavelength division multiplexer, and are transmitted along a single fiber. In a variation, a wavelength division multiplexer also allows two-way transmission along the same fiber by using different wavelengths in either direction. A WDM system, however, is limited by the number of separate wavelengths capable of being generated by the separate sources.
In light of the above-cited prior art, therefore, there remains a need for an optical multiplexer and demultiplexer capable of operating in a high-capacity optical fiber communication system.